DAYS of easy hunting are over for the submarine. Today the once-dreaded underwater craft must do battle, with the odds against them. The convoy system, adopted late in the World War, has deprived submarines of casy stalking of merchant ships, forcing them to attack in the presence of their deadliest enemy - the destroyer. Back in 1917, Kapitan-Leutenant Gustav Amberger had been ordered: “Remain out until all torpedoes are expended.” And the German admiralty demanded a shipmfor each torpedo. So Amberger, facing the perils of attack under the convoy system, kept the “U-58" outside Queenstown harbor two days, waiting for victims. At last came two destroyers, followed by eight ships in single file. Through the periscope, Amberger watched them. Submerged to fifty feet, with only an occasional peek through the upthrust eye, he maneuvered the “U-58” to intercept. They came at him in four rows of two each, the destroyers curving among them. Half an hour of tense waiting, of listening at the hydrophone to the increasing beat of propellers, while the “U-58" cruised submerged. Then a sharp order: “Up periscope!” A quick look and Amberger barked orders to the torpedomen, for there was the “Welshman,” a splendid freighter, plowing into position 300 yards off his bow. A torpedo could not miss. Amberger walked the periscope around to select the next victim, before revealing his presence by attacking the first ship. But even the first torpedo was never fired. That swing of the periscope had revealed a destroyer curving down upon him. Aboard the “Fanning,” one of two American destroyers convoying the merchant ships, Coxswain David D. Loomis scanned the water from his lookout post. Suddenly his sharp eyes caught something moving - a feathered, V-shaped wake. “Periscope!” Lieutenant Walter S. Henry sprang to the engine telegraph, barked “Rudder hard right!” at the helmsman, and the “Fanning” leaped into a swooping curve. Swiftly it bore down on that fleck of foam on the surface. The flick of a lever, and a depth charge went over the stern, exploding so violently the destroyer’s own generators were disabled. The crash brought the other destroyer, the “Nicholson,” dashing through the now furiously zigzagging convoy. The two destroyers swept in widening circles, while violent fountains spouted in their wakes. Fifteen minutes of blasting the depths gave no evidence of a hit. Down under, the “U-58" lurched wildly at the first crash, Kapitan-Leutenant Amberger stared anxiously at quivering needles on the instrument board. He ordered all stations to report. No leaks. Controls still worked. Motors, badly jarred, but still turning, could probably be fixed in a short time. Between the jar of explosions, Amberger ordered a quick dive to greater depth. One hundred feet. One-fifty. Two hundred. The engineer reported the engines had stopped. “Could they rest on the bottom while they were fixed?” No! Too deep! The cold black water would crush the boat. Two hundred and fifty feet! The diving officer reported headway was lost, the hydroplanes no longer acted. The game was up. Either they had to go down and be drowned, or rise and face the guns of those destroyers. Amberger chose the mercy of American sailors over that of the sea and ordered the tanks blown. American tars were amazed to see the submarine’s stern suddenly break surface at a sharp angle, settle back as the conning tower and the hull appeared. Quickly guns were remanned, shots were fired, the “Nicholson” hastily ran up and dropped a depth charge. Then out of the conning tower hatch crawled thirty men, arms upraised in surrender. Once again the strategy of the convoy had been proved. Already in the current hostilities, Britain and France have reorganized the convoy system. Tonnage figures demonstrate that submarine warfare can cause losses and force the employment of hundreds of ships, thousands of men, to combat it, but the easy hunting is gone. First defense against the U-boat is the mine field, sown outside harbors where subs are based. Mines are laid usually at night by submarines and trawlers, protected by destroyers and cruisers. They sink few subs, these mines, for they are swept up almost as fast as planted by trawlers. and drifters. But they hamper the U-boat’s movements; for frequently it takes two or three days to get one safely in or out of harbor. During the World War the British admiralty plotted on a chart the approximate position of every U-boat, frequently posting its number, and the name of its commander. This information came from Naval Intelligence agents at the very bases of the U-boats. And sweeping operations caused enough delay so this information could reach London in time to be of use. After a sub broke clear, its own radio gave it away, for whenever the radio spoke, direction finders got a fix, promply posted on the admiralty chart. Then, too, subs were constantly being sighted by fishing and patrol craft, or prospective victims. When a ship was attacked, its position was flashed before the victim plunged to its doom. Then why weren’t these U-boats sunk, if their location was known? Well, many were hunted down by plane and destroyer; | but that is not so simple. It is one thing to draw a twenty-mile circle on a chart and say a submarine was there at 11:30 a.m. It is quite another to arrive in a destroyer two hours later and find that submarine. For a sub can become invisible at will. On the hunt for prey, it cruises on the surface day and night, recharging the batteries on which it must operate when submerged. Lying low in the water, it can spot an enemy or victim ten to fifteen miles away, while it cannot ordinarily be spotted at farther than four or five miles. But a submarine’s invisibility ceases, temporarily, the moment it attacks. To use its deck gun, or board a ship to sink it with time bombs, it must come to the surface. The moment a torpedo is launched, the exhaust from its compressed-air motor leaves a telltale wake easily seen from a ship. The end of that wake marks the location of the submarine the moment the torpedo was fired. The submarine’s speed, submerged, is only six to ten knots, so it takes an appreciable time to get very far from the end of that wake. On this fact the convoy system is founded. It forces the submarine to attack in the presence of swift destroyers, which can dash down that wake and sow depth bombs before the sub has time to get far enough away for safety. The submarine cannot fight on anything like equal terms with a destroyer. Its narrow deck is a most unstable gun platform, making gunfire extremely erratic. A fishing smack armed with only a three-pounder has been known to defeat a U-boat, simply because the latter’s crew could not make enough hits with its heavier gun before its fragile hull was riddled. A destroyer mounts heavier guns than a sub, and more of them; can move fast enough to select its own position and range, and can absorb many hits and still fight back. But any kind of a hit on a submarine will deprive it of power to submerge. It is extremely difficult to torpedo a destroyer, because of its speed, ability to maneuver, and shallow draft. A torpedo moves through the water under its own power - a compressed-air motor. A gyroscope and fins hold it on a straight course. It is set to run submerged at a certain depth, usually about fifteen feet, and has a mechanism for maintaining that depth. If it runs too shallow, wave action will deflect it; and the depth required to insure its running true is greater than the draft of a destroyer - hence it frequently would pass under such a vessel without doing damage. Even in smooth water, where the torpedo need not run so deep, the speed of the destroyer will protect it. For a torpedo runs only forty to sixty miles an hour and can be avoided if its wake is seen in time. One American contribution to the anti-submarine campaign was the sub-chaser, with its hydrophones. These chasers, operating in threes, would patrol sub-infested waters, listening for the characteristic sound of the U-boat’s propeller. Having heard it, each of the trio would note the direction, lines would be plotted to obtain a fix, and the speedy little craft would dash to the scene, obtain another fix, then strew the area with depth bombs. In the World War, 100 allied subs sank twenty U-boats, a better batting average than any type of surface craft obtained. Sub against sub was not a case of the blind groping after the blind, Submarines must spend more time on the surface than submerged, coming up to recharge batteries, so they can run under water. A sub cannot stay under without its electric motors driving it forward, any more than an airplane can stay up when its motor stops. Once the motors stop, a sub must either fill its ballast tanks and sink to the bottom, or blow them, and come up. In enemy waters, its commander never knows when he will be forced to make an emergency dive, and a long, submerged run. Therefore he must strive constantly to stay on the surface, so his batteries will have full charge when needed. The defending sub is not in this constant danger; it may recharge batteries at night, cruise submerged most of the day, keeping watch through the periscope. It can thus see the rival submarine, with its conning tower and deck exposed, without being seen; can steal up and discharge a torpedo into the fragile side of its unsuspecting opponent.